A Tornado in Space (2)
Remembering Hannes Alfvén’s Admonition
In the twentieth century, astronomers showed
only a limited appreciation of plasma phenomena. Most ignored the
role of electric currents in space plasma, a subject unfamiliar to
them. As a result, the cascade of more recent observations has left
astronomers grasping for explanations.
In our previous Picture of
the Day we noted the mystery of
Herbig Haro 49/50,
conventionally described as a star-born “cosmic tornado” exhibiting
attributes that are, in astronomers’ words, “poorly understood”.
Attempts to explain the jets using standard astronomical models have
consistently failed to give plausible answers. What force is capable
of producing high-energy jets spanning light-years?
And by what means are these jets confined to a narrow stream
across such distances? Jetting stars, now observed by the hundreds,
find no comfortable place in the lexicon of traditional astronomy.
The only known
force that can prevent a stream of gas from rapidly dispersing in
the vacuum of space is magnetism, and only electric currents can
generate a magnetic field. But early in the twentieth century, the
community of astronomers had already settled on the idea that
gravity and inertia rule the heavens. Having constructed a simple
and secure vision of the cosmos, they were not eager to entertain a
more exotic force except as an inferior consideration, a footnote to
a mathematically elegant “big picture” of the cosmos.
The enigma is highlighted by
the top picture above: 1500 light-years from Earth lies “Herbig Haro
111”, displaying a jet 12 light-years long with
charged particles accelerated to speeds approaching 500 kilometers
per second. The finely filamentary and knotted jet spans
three times the distance from the Sun to our nearest star.
The authors of a Hubble
Telescope webpage discussing stellar jets have unintentionally
highlighted the present strains on the astronomers’ vision. They
seek to account for the “collimated” or narrowly confined jets in
terms of a “nozzle” located on one end—an explanation defying all
that science has learned about gases in a vacuum. The strains are
inescapable. We see them, for example, when the authors of the
Hubble page acknowledge that magnetic fields “might focus the
gas into narrow beams”. To this possibility, they respond, “there
is as yet no direct observational evidence that magnetic fields are
Eventually most astronomers
have come to acknowledge the ubiquitous presence of magnetic fields
in space. But in the face of this acknowledgement, how could they
preserve their foundational principle, which implies that
electricity does not “do anything” in the macrocosm?
For a time astronomers
thought they had an ally in the brilliant electrical engineer,
Hannes Alfvén, to whom all of modern physics is indebted for
new insights on the role of electric and magnetic fields in plasma.
Alfvén’s contributions were based on pioneering laboratory
research. In his early papers, he spoke of magnetic fields being
“frozen” into neutral plasma. To this notion astronomers were
readily attracted! It meant that plasma in space could have been
magnetized in primordial times or in early stages of stellar and
galactic evolution, all under the control of higher-order
gravitational dynamics. Every
energetic event could still be explained in terms of disconnected
islands of matter moving solely within the grip of gravity.
early assumption, astrophysicists began to study magnetized plasma
without having to seek out larger electric currents. They came to
view electric currents as localized and temporary phenomena needed
just long enough to create a magnetic field, to magnetize
plasma, the “perfect conductor”. Today, Alfvén’s concept of magnetic
fields “frozen-into plasma” underpins most mainstream
interpretations of magnetism in space. The approach enables
astronomers to look past the causative electric currents as if they
are no longer relevant. The study of magnetized plasma is now called
“magnetohydrodynamics”, and Alfvén is acknowledged as the founder of
the study. In 1970 he received the Nobel Prize for his “fundamental
discoveries in magnetohydrodynamics”.
The critical turn in this
story, the part almost never told within the community of
astronomers, is that Alfvén came to realize he had been mistaken.
And he used the occasion of his acceptance speech for the Nobel
Prize to plead with scientists to ignore his earlier work. Magnetic
fields, he said, are only part of the story. The electric currents
that create magnetic fields must not be overlooked, and contemporary
attempts to model space plasma in the absence of electric currents
will set astronomy and astrophysics on a course toward crisis, he
emphatically that plasma behavior is too “complicated and awkward”
for the tastes of the mathematicians. It is a field “not at
all suited for mathematically elegant theories”. It requires
hands-on attention to plasma dynamics in the laboratory.
Sadly, he observed, the plasma universe became “the
playground of theoreticians who have never seen a plasma in a
laboratory. Many of them still believe in formulae which we know
from laboratory experiments to be wrong”.
Again and again
Alfvén reiterated the point: the underlying assumptions of
cosmologists today “are developed with the most sophisticated
mathematical methods and it is only the plasma itself which
does not ‘understand’ how beautiful the theories are and absolutely
refuses to obey them”.
The theoretical crisis only
deepens as astronomers view the universe with higher-powered
telescopes and with instruments that “see” the entire
electromagnetic spectrum. Wherever they look, astronomers encounter
the effects of magnetic fields—a wild card that will inevitably
shatter the foundational assumptions of “standard” astronomy: Space
plasma cannot have a magnetic field permanently "frozen in" to it.
In a rarefied plasma environment, electric currents are required to
sustain a magnetic field. Herbig Haro objects—and innumerable other
structures in space—thus stand as a fundamental challenge to the
astronomers’ electrically sterile universe.
Decades ago, Alfvén showed that stars have an electrical circuit
involving an equatorial current sheet and polar current streams.
He noted that electromagnetic energy could be stored in a star's
equatorial current sheet until some critical juncture when that
energy is switched into a polar discharge. The resulting jet
would be energized by a particle-accelerating "double layer",
the wall of an insulating plasma sheath, across which there is a
strong electric field. In the presence of such an electric
field, the gravity of a star would give way to a force
incomparably more powerful than gravity, accelerating matter
away from the star. (A similar mechanism is now being
investigated for advanced plasma rocket engines).
Decades of laboratory experiments have shown that a toroidal
magnetic field, created by a polar plasma discharge, confines
the discharge to a narrow jet. In the vacuum of space, a
magnetic field will prevent the hot gases of a discharge from
rapidly dispersing and cooling like a wisp of steam. In the same
way, plasma experiments have shown that it is electrical energy
that creates and lights the bright knots and glowing filaments
along the path of the discharge. So the electrical theorists can
only scratch their heads when they see exclamations of surprise
and bafflement over the “mysteries” of interstellar jets. The
new discoveries simply confirm the findings of Alfvén and his
colleagues: Experiments in the plasma laboratory are scalable to
It is the common
sense of the electrical engineer, not elegant equations, that
exposes the obvious in Herbig-Haro objects. An axial electric
current, confined by a current-induced toroidal magnetic field, is
flowing along the entire length of the jet. Only an
electric field can accelerate charged particles across interstellar
space. There is no “nozzle” on one end accomplishing
the inconceivable. The jet is not defying good science, but
reinforcing it. And if the pictures speak more loudly than today’s
gravitational dogma, this is because interstellar space is alive
with electric currents.
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